It is the purpose of the proposed research to trace and identify, by a combination of ultrastructural and immunohistochemical techniques, some of the components of bacterial plaque that are thought to be of importance in inducing and maintaining inflammatory reactions in the gingiva. The penetration of these substances through gingival epithelium and connective tissue and the sites of reaction with local defense mechanisms will be studied in order to contribute to a better understanding of the etiology and pathogenesis of periodontal disease.